In the early part of the 2000s, I wrote a screenplay that briefly made the Hollywood rounds about a neurosurgeon who didn’t believe love, as it’s currently defined, actually existed. He was a clinical sort, and fell back on science and history to justify his beliefs. That’s not to say that he was unfeeling or uncaring. Quite the opposite. But he believed that what we call “love” was really just a chemical reaction in the deeply mammalian part of the brain that once stimulated our fight-or-flight response. Love, as he understood it, was a function to keep human beings together against menaces and to facilitate the continuation of the species. It was a survival instinct and nothing more. Sex was merely a reproductive exercise.

“Love” is a variety of different feelings and emotions, chemical brain states, and attitudes that ranges from interpersonal affection (“I love my mother”) to pleasure (“I loved that meal”). It can refer to an emotion of a strong attraction and personal attachment. It can also be a virtue representing human kindness, compassion, and affection—”the unselfish loyal and benevolent concern for the good of another.” It may also describe compassionate and affectionate actions towards other humans, one’s self or animals. Primarily, “love” is a social function that we’ve come to believe represents a mystical form of deep emotion for another. In short, the concept of “love” is supposed to make us feel good. And it does, as the emotion triggers brain regions similar to those that cause addiction and obsessive/compulsive disorders. It either satisfies that part of our biology, or triggers a negative reaction.

A study published in 2012 in the Journal of Sexual Medicine, analyzed 20 studies related to the effects of sex and love on the body. The research included brain scans of people who viewed erotic photos, photos of their significant others, food, and other pleasure triggers.

“Love” is a variety of different feelings and emotions, chemical brain states, and attitudes that ranges from interpersonal affection (“I love my mother”) to pleasure (“I loved that meal”). It can refer to an emotion of a strong attraction and personal attachment.

Two parts of the brain, the insula and the striatum, are responsible for tracking the way in which sexual desire develops into feelings of love, researchers said. Lust triggers parts of the brain that control pleasurable feelings, associated with sex and food, but love triggers parts of the brain associated with habits.

“The brain treats love like a habit that has been formed over time. So, after lust may come love, and those feelings of love move to different parts of the brain that processes habits and reward patterns. The same brain pattern occurs when people become drug addicts.”

Love in its various forms acts as a major facilitator of interpersonal relationships and, owing to its central psychological importance, is one of the most common themes in the creative arts.

Ancient Greeks identified four forms of love: kinship or familiarity (in Greek, storge), friendship (philia), sexual and/or romantic desire (eros), and self-emptying or divine love (agape). Modern authors have distinguished further varieties of romantic love. Non-Western traditions have also distinguished variants or symbioses of these states. This diversity of uses and meanings combined with the complexity of the feelings involved makes love unusually difficult to consistently define, compared to other emotional states.

Biological models of sex tend to view love as a mammalian drive, much like hunger or thirst. Helen Fisher, biological anthropologist and leading expert on the topic of love, divides the experience of love into three partly overlapping stages: lust, attraction, and attachment.

Lust is the feeling of sexual desire; romantic attraction determines what partners mates find attractive and pursue, conserving time and energy by choosing; and attachment involves sharing a home, parental duties, mutual defense, and in humans involves feelings of safety and security. Three distinct neural circuitries, including neurotransmitters, and three behavioral patterns, are associated with these three romantic styles.

Lust is the initial passionate sexual desire that promotes mating, and involves the increased release of chemicals such as testosterone and estrogen. These effects rarely last more than a few weeks or months. Attraction is the more individualized and romantic desire for a specific candidate for mating, which develops out of lust as commitment to an individual mate forms. Recent studies in neuroscience have indicated that as people fall in love, the brain consistently releases a certain set of chemicals, including the neurotransmitter hormones, dopamine, norepinephrine, and serotonin, the same compounds released by amphetamine, stimulating the brain’s pleasure center and leading to side effects such as increased heart rate, loss of appetite and sleep, and an intense feeling of excitement. Research has indicated that this stage generally lasts from one and a half to three years.

Biological models of sex tend to view love as a mammalian drive, much like hunger or thirst.

Since the lust and attraction stages are both considered temporary, a third stage is needed to account for long-term relationships. Attachment is the bonding that promotes relationships lasting for many years and even decades. Attachment is generally based on commitments such as marriage and children, or on mutual friendship based on things like shared interests. It has been linked to higher levels of the chemicals oxytocin and vasopressin to a greater degree than short-term relationships have. Enzo Emanuele and coworkers reported the protein molecule known as the nerve growth factor (NGF) has high levels when people first fall in love, but these return to previous levels after one year.

The Psychological Basis

Psychology depicts love as a cognitive and social phenomenon. Psychologist Robert Sternberg formulated a triangular theory of love and argued that love has three different components: intimacy, commitment, and passion.

Intimacy is a form in which two people share confidences and various details of their personal lives, and is usually shown in friendships and romantic love affairs. Commitment, on the other hand, is the expectation that the relationship is permanent. The last and most common form of love is sexual attraction and passion. Passionate love is shown in infatuation as well as romantic love. All forms of love are viewed as varying combinations of these three components.

Non-love does not include any of these components. Liking only includes intimacy. Infatuated love only includes passion. Empty love only includes commitment. Romantic love includes both intimacy and passion. Companionate love includes intimacy and commitment. Fatuous love includes passion and commitment. Lastly, consummate love includes all three.

Psychologist Erich Fromm maintained in his book The Art of Loving that love is not merely a feeling but is also actions, and that in fact, the “feeling” of love is superficial in comparison to one’s commitment to love via a series of loving actions over time. In this sense, Fromm held that love is ultimately not a feeling at all, but rather is a commitment to, and adherence to, loving actions towards another, oneself, or many others, over a sustained duration. Fromm also described love as a conscious choice that in its early stages might originate as an involuntary feeling, but which then later no longer depends on those feelings, but rather depends only on conscious commitment.

The Evolutionary Basis

Evolutionary psychology has attempted to provide various reasons for love as a survival tool. Humans are dependent on parental help for a large portion of their lifespans compared to other mammals. Love has therefore been seen as a mechanism to promote parental support of children for this extended time period. Another factor may be that sexually transmitted diseases can cause, among other effects, permanently reduced fertility, injury to the fetus, and increase complications during childbirth. This would favor monogamous relationships over polygamy.

Many different theories attempt to explain the nature and function of love. Explaining love to a person who had not himself or herself experienced love or being loved would be quite difficult because to such a person love would appear to be quite strange, if not outright irrational, behavior. Among the prevailing types of theories that attempt to account for the existence of love are: psychological theories, the vast majority of which consider love to be very healthy behavior; evolutionary theories which hold that love is part of the process of natural selection; spiritual theories which may, for instance consider love to be a gift from a god; and theories that consider love to be an unexplainable mystery, very much like a mystical experience.

So, in the centuries since humankind has attempted to define love, it comes down to this:

It’s all in our heads.

In the 21st century, we have assigned many romantic and theoretical ideologies to the word love. This may be the evolutionary equivalent of keeping the species together, procreating, and alive. After all, we are biological beings, and at the mercy of what our minds and bodies dictate. So the next time you feel “love at first sight,” stop and think about what it is you’re really feeling.

Stendhal, in his book On Love (“De l’amour”; Paris, 1822), distinguished carnal love, passionate love, a kind of uncommitted love that he called “taste-love”, and love of vanity. Denis de Rougemont in his book Love in the Western World traced the story of passionate love (l’amour-passion) from its courtly to its romantic forms. Benjamin Péret, in the introduction to his Anthology of Sublime Love (Paris, 1956), further distinguished “sublime love”, a state of realized idealisation perhaps equatable with the romantic form of passionate love.

“A writer, or any man, must believe that whatever happens to him is an instrument; everything has been given for an end. This is even stronger in the case of the artist. Everything that happens, including humiliations, embarrassments, misfortunes, all has been given like clay, like material for one’s art. One must accept it. For this reason I speak in a poem of the ancient food of heroes: humiliation, unhappiness, discord. Those things are given to us to transform, so that we may make from the miserable circumstances of our lives things that are eternal, or aspire to be so.” ― Jorge Luis Borges, Selected Non-Fictions